This invention relates to a cellular drum filter for the dewatering of fiber suspensions, and particularly relates to such a filter of the type including a trough for receiving the suspension and a filter drum rotatably supported in the trough in such a manner as to dip into the suspension therein. Vacuum suction is applied from within the filter drum to a portion of the drum's water pervious cylindrical surface, so that the liquid of the suspension is drawn through the drum, leaving a solid cake of fibers in the suspension on the outer surface of the drum.
Such drum filters are used primarily for the dewatering of fiber suspensions of pulp in the production of paper, cardboard, and the like. However, they can also be used in the sugar, chemical and cement industries, etc.
The vacuum suction can be produced, for instance, by the aspirating action of the water as it is discharged through a barometric tube, or by a vacuum pump. The vacuum suction is controlled by a valve arrangement located in each case over the part of the circumference of the drum from which the filtered, caked on material formed on the drum is removed, as a result of which atmospheric equalization of pressure takes place in that zone. It is known to connect a pipe to each of a plurality of suction cells underlying the cylindrical surface of the drum and to conduct all of the pipes to one end of the drum (or to conduct half of the pipes to each end). The vacuum suction is applied to a desired portion of the outer surface of the drum via pipes leading to the suction cells underlying that portion of the surface. A control head is disposed at one or both ends of the drum. It connects the pipes, to which suction is to be applied at any given time, with a common discharge pipe and with the vacuum suction producing device, and the control head covers the ends of the pipes to which suction is not then to be applied, to block application of the suction thereto. Such an apparatus includes an extremely large number of pipes, is difficult to manufacture, and is expensive. Access to the pipes is difficult, which is disadvantageous, particularly when it is necessary to repair leaks within the drum. In the event of a leak, the suspension liquid will pass into the interior of the drum. But this must be prevented because of the likelihood of corrosion. Immediate repair of a leak is therefore necessary. Furthermore, the frictional losses due to movement of the liquid in the pipes are relatively high.